Thin film development on a double layer of fluids over a stretching sheet

Abstract This research investigates two layers of immiscible fluids over a stretching sheet, where the primary layer is a Newtonian fluid and the secondary layer is a non-Newtonian second-grade fluid. The governing equations describing the flow are the two-dimensional mass and momentum equations supported by the interface and boundary conditions. The small aspect ratio of the fluid domain allows the application of long-wave theory and thereby two partial differential equations for the dynamics of thin liquid film for each layer are obtained. The coupled partial differential equations thus obtained are solved numerically by the finite volume approach where the spatial derivatives are approximated using the upwind difference scheme and the time derivatives are by forward difference. The study focuses on analyzing the impact of fluid processing parameters like Reynolds number, viscosity ratio, non-Newtonian parameter, and surface tension on the flow dynamics. The study reveals that the non-Newtonian parameter delays the thinning effect of the fluids across the fluid layers and may have possible applications in coating technologies, biomedical devices, and advanced manufacturing.